Separation of solids having different specific gravities



Dec. 13, 1960 w. c. EVANS ET AL 2,964,138

SEPARATION OF souns HAVING DIFFERENT SPECIFIC GRAVITIES Fild May 13,1957 Figl INVENTORS W/'///am C. Evans Eagmond 5-. Me uberg A tho/naySEPARATION OF SOLIDS HAVING DIFFERENT SPECIFIC GRAVITIES William C.Evans, 112 /2 NW. 18th, Oklahoma City, Okla., and Raymond E. Neuberg,2601 Robin Road, Midwest City, Okla.

Filed May 13, 1957, Ser. No. 658,595

2 Claims. (Cl. 209-453) This invention relates generally to improvementsin methods and apparatus for separating solids, and more particularly,but not by way of limitation, to an improved method and apparatus forseparating gold from sand.

The time-honored method of separating gold from sand by prospectors isby panning, wherein sand and water containing a minor proportion of golddust is moved through and around a suitable pan until all of the sand iswashed from the pan and only the gold remains. The pan is manipulated byhand and is variously tilted in all directions in an efiort to wash thesand away from the gold. This method is economical from an apparatuspoint of view, but a substantial amount of water is used and the methodis extremely time consuming and tedious, with the results always beingquestionable.

Several devices have also been designed to wash the sand away from thegold by a centrifugal action. In these devices, water and the sandcontaining the gold are poured into a vessel which ordinarily hassloping sides, with circumferential ridges in the sloping side walls.The vessel is rotated about its center, usually at a substantial speed,whereby the water and solids are thrown to the outer wall of the vesseland the water tends to wash the sand up over the edges of the vessel. Inthese devices the gold is supposed to stay either in the bottom or inthe ridges of the vessel side walls, with all of the sand being washedover the sides of the vessel. However, a portion of the gold isfrequently carried with the sand and is lost in the separation process.Many of these devices also utilize means for retaining a body of mercuryin the sides of the vessel to trap the gold as the vessel is beingrotated or spun. In these devices, the gold is amalgamated and issubsequently distilled from the mercury. Extremely intricate retainingdevices have been designed to retain the mercury in the desired locationin the vessel, but, to the best of our knowledge, none of these deviceshave been widely accepted.

The present invention contemplates a novel method of separating theheavier of at least two solids from a mixture of the solids by using aliquid carrier, and is particularly adapted to the separation of goldfrom sand with the use of Water. The method utilizes centripetal forceto provide a separation of the desired solid and facilitate draining ofithe liquid and the lighter of the solids. In a simple embodiment of thisinvention, I contemplate the use of an open-topped vessel which may berotated about its center, and which has a drain or outlet in the centralportion of the vessel. Sand, water and gold deposited in the vessel arefirst subjected to centrifugal force to move all of the materials towardthe outer periphery of the vessel. The water is then subjected tocentripetal force, whereby a portion of the water rushes to the centerof the vessel and is drained through the outlet. The water carries thelighter solids along with it to the center of the vessel for dischargethrough the outlet. The materials are laternately sub- States Patent2,964,188 Patented Dec. 13, 1960 jected to centrifugal and centripetalforce to provide a gradual step-by-step draining of the water andlighter solids, with the heavier solids remaining in the outer portionof the vessel. When used by prospectors, the vessel can be rotated andstopped by hand to provide the alternating centrifugal and centripetalforces, thereby requiring very simple apparatus and enabling theprospector to constantly View the separation process.

An important object of this invention is to provide a simple method ofseparating solids of different specific gravities requiring the use ofsimply constructed and economical apparatus.

Another object of this invention is to provide a method of separatinggold from sand which may be practiced with a minimum amount of training.

A further object of this invention is to provide a method of separatinggold from sand which may be carried out manually by a prospector in aremote location.

Another object of this invention is to provide an increase in speed overpresent methods of separating gold from sand.

A still further object of this invention is to provide a precise methodof separating gold from sand, wherein none of the gold will be lost inthe separation process and the water used in the process can be savedand used over and over if desired.

Other objects and advantages of the invention will be evident from thefollowing detailed description, when read in conjunction with theaccompanying drawings which illustrate our invention.

In the drawings:

Figure 1 is a plan view of one type of apparatus which may be used inpracticing the method of this invention.

Figure 2 is a vertical sectional view taken along lines 2-2 of Fig. 1.

Figure 3 is a plan view of a vessel illustrating a typical distributionof various solids in the vessel during a separation of the solids inaccordance with this invention.

Figure 4 is a schematic plan view of a modified apparatus which may beused in practicing this invention.

Referring to the drawings in detail, and particularly Figs. 1 and 2,reference character 6 generally designates an open-topped vessel havinga circular cross-section, with slightly tapered side walls 7. A suitablehandle 8 is secured in the top portion of the vessel 6 to faciliatespinning or turning the vessel, as will be more fully hereinafter setforth. The side Walls 7 of the vessel 6 may be either sloping outwardly,as shown, or of any other desired configuration, such as being trulyvertical. It is preferred that the bottom it) of the Vessel 6 have aplurality of concentric circumferential ridges 12 formed in the upperface thereof. The ridges l2 facilitate separation of solids deposited inthe vessel 6, and may take any desired configuration, such, for example,as circles, or radially extending ridges (not shown). However, thepresent method may be practiced with a vessel having a substantiallyflat bottom, as will be more fully hereinafter set forth.

A drain pipe 14 is provided in the center of the bottom 10 of the vesseland preferably extends no higher than the top face of the bottom 10.Thus, solids moved to the center of the vessel 6 will easily enter theupper end of the outlet 14. A suitable stop-per or plug 16 is insertedin the upper end of the outlet 14 to prevent loss of liquid and solidsfrom the vessel 6 prior to rotation of the vessel.

The vessel 6 is preferably supported on a table 18 through the use ofsuitable annular-shaped bearings 20 in such a manner that the vessel 6may be rotated about its center. The bearings 20 may be of any suitabletype which will permit relatively free rotation of the vessel 6. Thetable 18 is supported by legs 22 and has a bore 24 in the centralportion thereof located directly below the outlet pipe 14. When it isdesired to conserve water in practicing this invention, a second vessel26 may be placed below the table 18 directly underneath the bore 24, Thevessel 26 will, of course, be open-topped to receive liquid and solidsfalling through the outlet pipe 14 and bore 24.

In operation, the stopper 16 is inserted in the upper end of the outletpipe 14 in the manner shown, and a liquid containing the solids to beseparated are poured into the vessel 6. It will be assumed that thevessel 6 is being used to separate gold from sand and that the solidsare carried by water. The proportion of sand to water poured into thevessel 6 can be varied through wide limits, depending principally on theskill of the operator. We have found that when using a vessel about teninches deep, with a diameter of about ten inches at the bottom andtwelve inches at the top, the invention can be practiced efl'iciently bypouring about a one inch layer of sand in the bottom of the vessel and alayer of about five inches of water above the sand. It will be assumedthat the sand contains a minor proportion of finely divided gold.

The vessel 6 is then rotated about its center at a speed suflicient tomove the water to the outer portion of the vessel as illustrated by thedashed lines in Fig. 2. The sand and gold will, of course, be moved tothe outer portion of the vessel 6 by centrifugal force along with thewater. When the water has moved outwardly away from outlet pipe 14, thestopper 16 is removed. The speed of the vessel 6 is then decreased; andthe water, which will then move in a substantially circular orbit in thevessel, wiEl. provide a washing action toward the outlet pipe 14 by theaction of centripetal force. A portion of the sand will be carried bythe water toward the center of the vessel 6 and will flow down the drainpipe 14, along with a portion of the water. The gold, being heavier thanthe sand, will tend to remain on the bottom 10 in the outer portion ofthe vessel. However, if the sand starts moving toward the center of thevessel at a substantial speed, the sand will tend to carry the goldalong with it out through the pipe 14. Therefore, when the sand startsmoving toward the outlet pIpe 14 at a depth which would obscure thepresence of gold in the sand, the speed of the vessel 6 is againincreased to move the sand and water back toward the outer periphery ofthe vessel by centrifugal force. Also, the water must be kept incircular motion to provide the desired centripetal force. Thus, thevessel should again be rotated before the water stops turning.

When the speed of the vessel 6 is again such that the water is outwardlyof the pipe 14, the speed of the vessel can be decreased to provide afurther drainage of water and sand through the outlet pipe 14. Thesealternating steps are repeated until all, or substantially all of thesand is removed through the outlet pipe 14. When all of the water hasbeen removed from the vessel without removing all of the sand, thesolids will be in the positions illustrated in Fig. 3. The small circlesindicate sand grains which will be arranged around the outlet pipe 14 inthe central portion of the vessel 6; whereas the gold, indicated bysmall triangles, will be located near the outer periphery of the vessel6. The Xs indicate a third solid, as described below.

As it is well known, some grains of sand are frequently about the samecolor as gold, making it difiicult to see particles of gold in sand,even though the sand may contain a substantial proportion of gold. Itwill thus be apparent that when the speed of the vessel 6 is beingcontrolled manually through viewing the movement of sand in the bottomof the vessel, there is the constant possibility that the water will besubjected to a centripetal force too long in a single step and that someof the gold will be carried out through the outlet pipe 14 with thesand. Tofacilitate the visual control of the movement of the solids,another solid having a specific gravity between sand and gold and acolor strikingly different from. both sand and gold may be mixed withthe solids at the beginning of a separation operation. We have foundthat finely divided lead is particularly useful. The lead has a specificgravity between sand and gold and is sufficiently dark that it can beeasily identified in sand in relatively minor proportions. When usinglead or the like, the lead will tend to move toward the outlet pipe 14ahead of the gold and behind the sand. Therefore, when slowing down thevessel 6 to provide a drainage of water and sand through the outlet pipe14, the operator can easily determine the approach of the lead to thecenter of the vessel 6. When the operator sees lead progressing towardthe center of the vessel, he can again increase the speed of the vesselto move the water and solids back toward the outer perIphery of thevessel. At the end of a separation operation using an indicator such aslead, the lead (indicated by small xs in Fig. 3) will assume a positionbetween the sand and gold because of its relative specific gravity.

In practicing the present method in the manner described above, thevessel 6 can easily be rotated manually by use of the handle 8. When thespeed of the vessel 6 should be increased, the operator merely placesone finger against the handle 8 and spins the vessel. When the speed ofthe vessel 6 should be decreased, the operator can use one or both handsagainst the side walls of the vessel in the manner of a brake until thespeed of the vessel should again be increased. The periods of subjectingthe water and solids to centrifugal force and, alternately, centripetalforce are controlled by the operator who will be watching the movementsof solids over the bottom lti ot' the vessel. With a little practice,any prospector can efiiciently separate the gold by the present method.It will be readily understood, however, that the periods of centrifugaland centripetal force may be controlled automatically when theapproximate proportions of gold, sand and water are known, andparticularly the proportion of sand to water. With experience inpracticing the method using uniform starting proportions of water andsand, the lengths of the periods may be precisely determined, and thenthe rotation and deceleration of the vessel 6 can be easily controlled,as by a mechanical drive system.

A further feature of note in practicing the method as above described,is that the water used in the method may be easily conserved and re-usedas many times as desired. The water draining through the outlet pipe 14will accumulate in the lower vessel 26 and can be poured back into thevessel 6 when a new operation is started. This feature is particularlyimportant to prospectors operating in extremely dry areas. With thismethod, substantially the only water which will be lost is throughevaporation.

As a modification of the method described above, we may use theapparatus illustrated in Fig. 4. In this embodiment of the invention,the water is supplied to the vessel 6 by means of a hose 28 and nozzle3%. The nozzle 30 is arranged horizontally and substantially on atangent with the inner periphery of the side walls 7 of the vessel,whereby water is introduced into the vessel on atangent as illustratedin Fig. 4. It will be apparent that water injected into the vessel inthis manner will tend to flow circumferentially around the vessel 6.With the vessel 6 supported on bearings, such as the bearings 20 in Fig.2, the water injected through the nozzle 30 will, by friction, drive thevessel in a rotating movement. The solids will normally be deposited inthe vessel prior to water injection.

When the speed of the vessel equals the speed of the water, the solidswill be subjected to a predominantly centrifugal force and will tend tomove to the outerperiph-- cry of the vessel. However, when the angularspeed of the water in the vessel exceeds the speed of the vessel,centripetal force created by the water tends to wash the solids towardthe center of the vessel in the same manner as previously described. Thesand, being lighter than the gold, will be washed ahead of the gold.When so much sand is being moved to the outlet 14 to obscure thepresence of gold, the speeds of the water and vessel are again equalizedto move the solids back out toward the outer periphery of the vessel.Water will, of course, be drained through the outlet 14 when subjectedto centripetal force.

The relative speeds of the water injected through the nozzle 30 andvessel 6 may be controlled in either of two ways. Firstly, the rate ofwater injection may be retained constant and a brake applied to orreleased from the vessel 6 to decrease or increase the speed of thevessel. Secondly, the vessel 6 may be left free to rotate at all. timesand the rate of water injection varied. In either event, the solids aresubjected to alternating centrifugal and centripetal forces toeffectively wash the sand from the gold. It will also be noted that therelative speeds may be automatically controlled, particularly when thespeed of the vessel is controlled by an external braking action.

Still another embodiment of the method of this invention is by turningonly the water, with the retaining vessel being held in a stationaryposition. In practicing the method in this manner, the vessel 6 issupported directly on a stationary table, such as the table 18, with theoutlet pipe 14 extending downwardly through the bore 24. The vessel 6will then be retained in a stationary position on the table. In thisembodiment, we prefer to rotate water in the vessel 6 by use of thenozzle 30 arranged as described above. As water is continuouslyinjected, the solids are poured into the vessel 6 near the outerperiphery. The speed at which the solids are poured into the vessel willdepend upon the speed of the water and the particle size of the solids;care being taken that too much of the lighter solid are not being addedto obscure a view of the movement of solids in the vessel when theoperation is manually controlled. The water, in being rotated in thestationary vessel 6, provides a centripetal washing action on the solidsto move the lighter solids toward the outlet 14 ahead of the heaviersolids in the same manner as described above.

Although we prefer to rotate the water by injecting the watertangentially into the stationary vessel, it will be understood that thewater may be turned or rotated by various means. For example, in a smallinstallation, the water may be rotated by the operator inserting hishand in the water and moving the hand around the inner periphery of theside wall 7. Also, the water may be turned by a suitable paddlemechanism (not shown). It is also to be noted that when only the wateris rotated, 'the solids will be subjected only to a centripetal washingaction.

In all of the various modifications of the present invention, the use ofridges in the bottom of the vessel 6, such as the concentriccircumferential ridges 12, facilitates separation of the sand and gold.The sand and gold will, of course, constantly tend to settle to thebottom of the vessel when the water is being rotated, as well as whenthe water is quiescent. When the vessel 6 is being rotated at asubstantial speed, the gold, being heavier than the sand, will tend tomove to the outer periphery of the vessel ahead of the sand. However,when the water is subjected to centripetal force, the sand will tend tomove before the gold. Thus, the sand will be carried toward the centerportion of the vessel 6 ahead of the gold, with the sand being rolledalong the bottom 10 of the vessel. The ridges 12 tend to reduce theinward movement of all of the solid materials, and particularly theinward movement of the gold, since the gold will be in substantiallyconstant contact with the bottom 10 and will have the least tendency tobe carried with the water. In other words, the ridges 12 retard theinward movement of the gold more than the inward movement of the sand.However, the centrifugal force of the gold will be substantial enough tomove the gold outwardly over the ridges 12 to the outer periphery of thevessel when the vessel is rotated at a sufficient speed to move thewater outwardly away from the outlet pipe 14.

From the foregoing it will be apparent that the present inventionprovides a simple method of separating the heavier of two solids from aliquid carrier by use of simply constructed and economical apparatus.The method is subject to extensive automatic control when theproportions of starting materials are retained constant. Also, themethod is particularly adapted for use by prospectors in remotelocations, and the water employed in the method may be re-used severaltimes without any substantial waste. It will also be apparent that thepresent invention provides a precise method of separating a minorproportion of gold from sand the gold may be separated in a minimum oftime. Also, a minimum of training is required to practice the method.

Changes may be made in the combination and arrangement of steps andprocedures heretofore set forth, it being understood that changes may bemade in the precise embodiments described without departing from thespirit and scope of the invention as defined in the following claims.

We claim:

1. A method of separating gold from sand and the like in a vesselcontaining such solids and water, comprising the steps of:

(a) mixing a third solid with the gold and sand having a density betweengold and sand and a color different from gold and sand,

(b) spinning the vessel about its center to move the water and solidstoward the outer portion of the vessel, and, alternately,

(c) reducing the angular velocity of the vessel until at least a portionof the water and sand move to the central portion of the vessel, and

(d) draining a portion of the water and sand from the central portion ofthe vessel each time the velocity of the vessel is reduced.

2. A method as defined in claim 1 characterized further in that saidthird solid is finely divided lead.

References Cited in the file of this patent UNITED STATES PATENTS184,622 Hooper Nov. 21, 1876 560,435 Seymour May 19, 1896 872,555 CappsDec. 3, 1907 1,795,017 Fischer Mar. 3, 1931 2,178,390 Bockel Oct. 31,1939 2,743,815 Goodwin May 1, 1956 OTHER REFERENCES Ganot: GanotsPhysics, Sixth Edition, William Wood and Company, N.Y., 1890, pages38-39.

Taggert, A. F.: Handbook of Mineral Dressing, 1945, chapter 19, page169.

